Facility and equipment rent expense.

No definition available.

Name:	arwr_FacilityAndEquipmentRentExpense
Namespace Prefix:	arwr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Leased facility expense.

+ References

No definition available.

+ Details

Name:	arwr_LeasedFacilityExpense
Namespace Prefix:	arwr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Other rental expenses.

+ References

No definition available.

+ Details

Name:	arwr_OtherRentalExpenses
Namespace Prefix:	arwr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Payments under capital lease.

+ References

No definition available.

+ Details

Name:	arwr_PaymentsUnderCapitalLease
Namespace Prefix:	arwr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of increase in annual rental cost.

+ References

No definition available.

+ Details

Name:	arwr_PercentageOfIncreaseInAnnualRentalCost
Namespace Prefix:	arwr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Date which lease or group of leases is set to expire, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_OtherCommitmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum amount of purchase arrangement in which the entity has agreed to expend funds to procure goods or services from a supplier.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the next fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationDueInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum amount of purchase arrangement maturing in the remainder of the fiscal year following the latest fiscal year ended. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

A segregation of retained earnings which is unavailable for dividend distribution. Includes also retained earnings appropriated for loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 31

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.30(a)(3)(i))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6403732&loc=d3e21332-112643

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.23(4))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 45

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6403732&loc=d3e21346-112643

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 24

-Subparagraph a(4)

-Article 7

+ Details

Name:	us-gaap_RetainedEarningsAppropriated
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Utilities costs incurred during the reporting period for services, such as water, sewer, gas, electricity and telephone required to operate a building.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.2)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

Name:	us-gaap_UtilitiesCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=arwr_CorporateHeadquartersInPasadenaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=arwr_ResearchFacilityInMadisonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Other Commitments [Line Items]
Facility and equipment rent expense	$ 191,000arwr_FacilityAndEquipmentRentExpense	$ 134,000arwr_FacilityAndEquipmentRentExpense	$ 362,000arwr_FacilityAndEquipmentRentExpense	$ 264,000arwr_FacilityAndEquipmentRentExpense
Provision for recorded liabilities	0us-gaap_RetainedEarningsAppropriated		0us-gaap_RetainedEarningsAppropriated
Future commitments	49,700,000us-gaap_PurchaseObligation		49,700,000us-gaap_PurchaseObligation
Commitments expected to be incurred in fiscal 2015	29,500,000		29,500,000
Commitments expected to be incurred beyond fiscal 2015	20,200,000		20,200,000
Corporate Headquarters In Pasadena
Other Commitments [Line Items]
Rental expense			23,000
Operating lease expiration date			Sep. 30, 2019
Percentage of increase in annual rental cost			3.00%
Research Facility in Madison
Other Commitments [Line Items]
Rental expense			26,000
Operating lease expiration date			Feb. 28, 2019
Other rental expenses including common area maintenance and real estate taxes			18,000
Utilities costs per month			16,000
Monthly payments under capital lease			19,000
Total Monthly Facility Expense - Madison facility			$ 79,000